An inkjet printer is usually equipped with a piezoelectric actuator. Due to a high-speed reciprocating motion of the piezoelectric actuator, the inkjet printer can eject ink droplets. Generally, the high-speed reciprocating motion of the piezoelectric actuator is driven by a high AC voltage. When the piezoelectric actuator is driven by the high AC voltage, the piezoelectric actuator continuously and periodically issues a control signal to a single-nozzle or multi-nozzle vibration plate. According to the control signal, the single-nozzle or multi-nozzle vibration plate is enabled to perform the reciprocating motion. Consequently, the ink droplet is ejected out through a single-nozzle or multi-nozzle inkjet head. That is, the piezoelectric actuator can be applied to an inkjet printer with the single-nozzle or multi-nozzle inkjet head. Moreover, the piezoelectric actuator can be applied to a micro-dispensing pipette such as a biochemistry medical laboratory instrument or industrial dispensing equipment.
Conventionally, the power supply for powering the piezoelectric actuator comprises a DC-DC converting circuit and a DC-AC converting circuit. Since the DC-DC converting circuit and the DC-AC converting circuit are discrete circuits, the conventional power supply needs not only a large number of electronic components but also a coil-type transformer. Under this circumstance, the area of the circuit board and the fabricating cost are both increased.
FIG. 1 is a schematic circuit block diagram illustrating a DC-AC converting circuit of a conventional power supply for powering a piezoelectric actuator. As shown in FIG. 1, the DC-AC converting circuit 100 comprises a timing generator 102, two switch elements Q102, Q104, a resonant circuit composed of a resonant capacitor C101 and a resonant inductor L101, and a transformer T102. According to a switching control signal provided by the timing generator 102, the switch elements Q102 and Q104 are alternately conducted or shut off, and thus the electric energy of the DC input voltage Vdc is transmitted to the primary side of the transformer T102. The resonant circuit (C101, L101) is used for generating resonance to transmit the electric energy of the DC input voltage Vac to the primary side of the transformer T102. According to the turn ratio of the primary winding to the secondary winding of the transformer T102, an AC voltage Vac is induced and outputted from the secondary side of the transformer T102. The AC voltage Vac is used for driving a piezoelectric actuator (not shown). Since the way of increasing the voltage is performed by adjusting the turn ratio of the transformer T102, the voltage-increasing capability of the DC-AC converting circuit 100 is usually insufficient to drive the piezoelectric actuator of the inkjet printer with the single-nozzle or multi-nozzle inkjet head.
FIG. 2 is a schematic circuit block diagram illustrating a DC-AC converting circuit of another conventional power supply for powering a piezoelectric actuator. As shown in FIG. 2, the DC-AC converting circuit 200 comprises a detecting circuit IC2, a switching control circuit IC1, two switch elements Q206, Q208, a transformer T1, and an output filter circuit (L1, L2, C6). The DC-AC converting circuit 200 is used for driving a piezoelectric actuator PZT. The detecting circuit IC2 is used for detecting an output voltage of the DC-AC converting circuit 200. According to the detecting result generated by the detecting circuit IC2, the switching control circuit IC1 generates a switching control signal to control the on/off statuses of the switch elements Q206 and Q208. By alternately turning on/off the switch elements Q206 and Q208, the electric energy of the DC input voltage Vdc is transmitted to the primary side of the transformer T1. In addition, by alternately turning on/off the switch elements Q206 and Q208, the electric energy of the DC input voltage Vdc is transmitted to the secondary side of the transformer T1. As a consequence, an AC voltage is outputted from the secondary side of the transformer T1. Moreover, after the noise contained in the AC voltage is filtered by the output filter circuit (L1, L2, C6), an output AC voltage is generated to drive the piezoelectric actuator PZT. Since a large number of electronic components and a coil-type transformer are necessary to constitute the DC-AC converting circuit 200, the performance of the DC-AC converting circuit 200 applied to the piezoelectric inkjet head is usually unsatisfied.